Ozone Depletion Drives Worlds Largest Mass Extinction

About 250 million years ago something occurred which led to the extinction of roughly 90% of all the species on Earth. This event also known as the Great Dying coincided with a massive volcanic eruption lasting almost 1 million years in what is now modern day Siberia, Russia. The so-called Siberian Flood Basalts have therefore been named the number one culprit for instigating the largest ever mass extinction on Earth. However there is still debate surrounding the exact link between volcanism and the almost complete disappearance of life on Earth.

Now a team of researchers led by the Universities of Manchester and Oxford have shed a new light on one of the probable causes of the mass extinction. In a new study published in Nature Geoscience, the team suggest that a massive volume of halogens was released to atmosphere during the prolonged volcanic eruption. Halogens injected in to the atmosphere resulting in the widespread destruction of the ozone layer. Without the protective ozone layer the Earth was exposed to deadly levels of ultra-violet radiation resulting in mutations, infertility and species extinction.

Schematic of plume–lithosphere interaction within the Siberian craton.

The team analysed sections of the lithosphere erupted to the surface both before and after the formation of the Siberian Flood Basalts. Dr Michael Broadley, the lead author from the University of Manchester, explains: “Before the massive eruption of the Siberian Flood Basalts we found that the lithosphere below Siberia was incredible enriched in halogens, chorine, bromine and iodine, but surprisingly, after the eruption the levels of halogens stored in the lithosphere were dramatically reduced.” Dr Peter Barry, co-author from Oxford University added “We concluded that the halogens must have been mobilised and transported to the surface by an upwelling mantle plume which was feeding Siberian volcanism, with devastating consequences to the Earth ozone layer and life on Earth.”

This project was funded in part by the European Research Council FP7 ‘NOBLE’ grant to Chris Ballentine. Find out more about the Noble lab.

Sketch Up of the Volatile Siberian trap eruptions, by James Tuttle Keane, Nature Geoscience (2018)